Photodetectors are used for image detection, in particular to monitor activity such as movement or other changes in the image being detected. Output of photodetectors is often used as the input for image processing in order to initiate responses to what is detected. Among other applications, photodetectors are commonly used in biosensors for medical diagnostic and related fields. Current photodetection technology uses silicone-based and photochromic-based detection systems.
There are a number of limitations to current photodetection technology. Existing photodetectors are generally damaged by high energy levels, including high levels of incident light. They generally also exhibit a lack of detection sensitivity and a limited detection range. This lack of sensitivity can make coupling of specific inputs to specific outputs difficult, meaning there is no "fine tuning" Existing photodetectors are restricted to rigid materials for detection and display. There are also maximum size limitations for the detectors themselves and for arrays of detectors. In addition, the most stable photochromic materials currently used darken in response to light rather than having optical densities which decrease as light intensity increases.
Recently methods have been sought to utilize photodetection technology for dynamic camouflage applications. The goal is to develop a color display capable of changing pattern and color with similar changes in the surrounding environment. The current method of providing camouflage is permanent coloring of the object to be camouflaged. The limitations of current photodetection technology when applied to camouflage applications include the limited range of light intensity which can be detected, the limited amount of color discrimination which is available, the lack of robustness of current technology photodetectors, the inability to apply the photodetectors in conformal coatings, and the fact that the change in color of current photochromic materials is in the "wrong" direction.
The photovoltaic properties of certain proteins has been previously known, but these proteins have not been utilized in photodetector technology. Use of photodynamic proteins in photodetectors could provide several advantages. They would allow a broad photodynamic detection range and possibly increased robustness (ruggedness) over current photodetectors. They would also give the ability to form detectors or arrays of unlimited size. In addition, multi-component photodynamic protein-based photodetector groups can be tailored to receive specific wavelengths of light. Certain photodynamic proteins also exhibit the desired direction of color change in response to light intensity, such that optical density decreases as light intensity increases, which would allow their use for photochromic display applications such as camouflage. Photodynamic protein-based photodetectors could also be used in conformal coatings.